The present description relates to an internal combustion engine, more particularly relates to a method of starting an internal combustion engine without excessive engine speed increase.
There is shown and presented, for example in Japanese patent application publication no. 2004-308570A, a method of starting an engine of a hybrid electric vehicle. Generally, the hybrid electric vehicle more frequently stops and restarts the engine, and therefore, when restarting the engine, it requires smoother engine start. Particularly, the method of '570 publication seeks suppression of a vibration caused by compression of air in the combustion chamber during motoring the engine (without supplying fuel). When starting the engine, an electric machine first cranks the engine at an engine speed with advanced intake valve timing in order to purge the air in a surge tank of the engine. Then, it motors the engine at an increased speed with retarded intake valve timing in order to reduce an effective compression ratio by reducing air charge in the combustion chamber with the retarded intake valve timing.
According to the method, at the second stage of the motoring the engine, the reduced effective compression ratio may suppress the vibration caused by the compression of air. However, in supplying fuel and starting combustion of the fuel after the second stage, the engine speed may increase excessively. In theory, if the closing timing of the intake valve is constant after a bottom dead center of an intake stroke of an engine cycle, the amount of air charged into the combustion chamber increases as the engine speed increases. According to the prior art method, after the combustion has begun, the engine speed increases so as to increase the air charge and engine torque derived from the combustion of the increased air charge. The increased torque may further increase the engine speed, and eventually the excessive engine speed increase may occur. It may cause a torque disturbance or require a complex control of the electric machine to suppress the torque shock.